Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.55   10.725%   $239.775   $239.78   $239.80   $239.80  
  Purchase #2 $56.51   6.523%   $60.1961   $60.20   $60.20   $60.20  
  Purchase #3 $144.63   8.167%   $156.4419   $156.44   $156.45   $156.40  
  Purchase #4 $50.90   5.818%   $53.8614   $53.86   $53.85   $53.90  
  Purchase #5 $204.84   10.310%   $225.959   $225.96   $225.95   $226.00  
  Purchase #6 $201.93   5.723%   $213.4865   $213.49   $213.50   $213.50  
  Purchase #7 $41.49   5.372%   $43.7188   $43.72   $43.70   $43.70  
  7 purchase totals = $916.85       $993.4387   $993.45   $993.45   $993.50